Downhole Seal

ABSTRACT

A downhole seal ( 10 ) comprises an inflatable structure ( 14 ) which receives a volume of swellable particles ( 18 ) at a downhole location. The seal ( 10 ) is adapted to permit the swellable particles ( 18 ) to become exposed to an activator to initiate selling of said particles ( 18 ) to inflate the inflatable structure ( 14 ).

FIELD OF THE INVENTION

The present invention relates to a seal, and in particular to a high expansion downhole seal, such as a packer.

BACKGROUND OF THE INVENTION

Many downhole oil and gas operations require seals to be established to provide fluid barriers within the well. It is often the case that the seal must be established in annular regions, such as between the outer surface of liner tubing and the inner surface of an open or cased bore. These annular regions may be sealed using packers, for example, and may be required for zonal isolation purposes and the like. Many focus of annular seals or packers are known, such as mechanical packers, inflatable packers, swellable packers and the like.

The construction and architecture of a conventional well, however, may make establishing effective downhole seals difficult. For example, many wells include a number of restrictions through which a seal assembly must pass before reaching the target seal location. Accordingly, the seal assembly must be capable of being configured with a small outer diameter to pass through the restrictions and then reconfigured to define a larger outer diameter to establish the necessary seal. In many cases the required expansion ratio is significant thus making it difficult to establish a sufficient seal.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a downhole seal comprising an inflatable structure adapted to receive a volume of swellable particles at a downhole location.

The seal may therefore be run into a wellbore in a deflated configuration, and once at the required depth the inflatable structure may be inflated by receiving the swellable particles to establish a downhole seal. This arrangement may therefore permit the seal assembly to initially describe a relatively small outer diameter when deflated, for example to pass through one or more wellbore restrictions, and then be inflated by receiving the swellable particles to describe a relatively large outer diameter to permit a high expansion ratio to be achieved.

The downhole seal may be adapted to permit the swellable particles to become exposed to an activator to initiate swelling of said particles. Accordingly, the inflatable structure of the seal assembly may be adapted to become inflated to establish a seal by a combination of receiving the swellable particles and swelling of the particles.

The activator may comprise a chemical activator, such as a fluid, for example a wellbore fluid. The wellbore fluid may comprise water, hydrocarbons, cement, mud or the like. The activator may comprise a chemical activator, thermodynamic activator, pressure activator, mechanical activator or the like, or any suitable combination thereof.

The inflatable structure may be adapted to permit fluid communication of an activator fluid therethrough to expose the swellable particles to said activator fluid. At least a portion of the inflatable structure may be permeable. For example, at least a portion of a wall of the inflatable structure may be permeable.

The inflatable structure may comprise an osmotic membrane, wherein a fluid may be communicated across said membrane by osmotic action. For example, the inflatable structure may be adapted to receive a fluid having a salt concentration which is higher than the salt concentration of a wellbore fluid, thus creating a concentration gradient to establish osmotic flow of the wellbore fluid through the osmotic membrane.

Alternatively, or additionally the inflatable structure may define at least one fluid port.

The seal may comprise a store of a swelling activator, such as a fluid, wherein the inflatable structure is adapted to receive the swelling activator from said store. The store of swelling activator may be provided at surface level. Alternatively, or additionally, the store of swelling activator may be provided in the region of the inflatable structure.

The seal may comprise a store of swellable particles, wherein the inflatable structure is adapted to receive swellable particles from said store. The store of swellable particles may be provided remotely from the inflatable structure. For example the store of swellable particles may be provided at a surface location and delivered downhole to the appropriate location of the inflatable structure.

Alternatively, or additionally, the store may be located adjacent the inflatable structure. In this arrangement the seal comprising the inflatable structure and the store of swellable particles may be run downhole into a wellbore to the required depth, and swellable particles transferred into the inflatable structure from the store.

The seal may comprise a communication passage between the inflatable structure and the store of swellable particles. The communication passage may comprise a non-return arrangement, such that swellable particles which have entered the inflatable structure may be prevented or restricted from returning to the store. The seal may comprise a displacing arrangement adapted to displace swellable particles from the store towards the inflatable structure. The displacing arrangement may comprise a piston assembly, pumping assembly or the like.

In one embodiment the seal may comprise a tubular body, wherein the inflatable structure may be mounted on the tubular body, for example externally of the tubular body. In this arrangement the inflatable structure may define a circumferentially contained space disposed around the tubular body.

The tubular body may comprise a store of swellable particles, such that swellable particles contained within the tubular body may be delivered to the inflatable structure to inflate said inflatable structure.

The tubular body may define a passage extending between the store of swellable particles and the inflatable structure. The passage may comprise at least one port extending through a wall portion of the tubular body. The at least one port may comprise a non-return arrangement adapted to prevent or restrict the swellable particles from re-entering the tubular body from the inflatable structure.

A displacing arrangement adapted to displace swellable particles from the store towards the inflatable structure may be mounted within the tubular body. In one embodiment the displacing arrangement may define a piston slidably mounted within the tubular body. The piston may be adapted to be hydraulically actuated, mechanically actuated or the like.

The displacing arrangement may be adapted to be configured to permit circulation of a fluid through the tubular body and past the displacing arrangement. For example, the displacing arrangement may comprise a piston, and the tubular body may comprise a region of increased diameter, wherein location of the piston within said region of increased diameter may permit by-pass of fluid.

Alternatively, the displacing arrangement may comprise a frangible region adapted to be released or removed to permit fluid by-pass.

The seal may comprise a slurry of swellable particles adapted to be delivered to the inflatable structure. The slurry may comprise a volume of swellable particles mixed with a fluid. The fluid may be selected to prevent swelling of the swellable particles. For example, the swellable particles may be benign within the fluid of the slurry. This arrangement may therefore prevent the swellable particles from swelling prior to being delivered into the inflatable structure.

The slurry fluid may comprise a high salinity water, oil or the like. In some embodiments this arrangement may permit osmotic transfer of fluids from the wellbore.

The inflatable structure may be adapted to permit release of the slurry fluid, thus permitting the swellable particles to become exposed to a swell activating medium. For example, the inflatable structure may be adapted to permit the fluid contained within the slurry to be released into the wellbore.

The inflatable structure may comprise a bag. The inflatable structure may be at least partially elastic, inelastic or the like. The inflatable structure may be initially folded or the like, such that the inflatable structure unfolds when inflated with swellable particles.

The inflatable structure may comprise a swellable material. For example, a wall portion of the inflatable structure may be at least partially formed of a swellable material.

The seal may be adapted to be run into a wellbore on a tubing string, such as a production tubing string, coiled tubing or the like. The seal may be adapted to be run into a well bore on wireline or the like.

The seal may define a packer.

According to a second aspect of the present invention there is provided a method of establishing a downhole seal, said method comprising the steps of:

locating an inflatable structure within a wellbore; and

inflating said inflatable structure with swellable particles.

The method may further comprise the step of exposing at least a portion of the swellable particles to a swell-activating medium. In this arrangement the inflatable structure may be inflated to establish a seal by the action of both filling the inflatable structure with the swellable particles in combination with swelling of the particles.

The method may comprise the step of running the inflatable structure through a wellbore restriction, and then inflating said inflatable structure.

The method according to the present invention may comprise the use of the downhole seal according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a downhole seal in accordance with an embodiment of the present invention, shown in a deflated configuration; and

FIG. 2 is a diagrammatic representation of the downhole seal of FIG. 1, shown in an inflated configuration.

DETAILED DESCRIPTION OF THE DRAWINGS

A downhole seal, generally identified by reference numeral 10, in accordance with an embodiment of the present invention is shown in FIG. 1. The seal 10 comprises a tubular body 12 which may form part of a tubing string used to convey the seal 10 into a well to the required depth. An inflatable structure 14 in the form of a bag is circumferentially mounted around the outer surface of the tubular body 12. The inflatable structure 14 is shown in FIG. 1 in a deflated configuration in which the bag defines a number of folds 16, such that the seal 10 may be configured with a relatively small outer diameter. In this configuration the seal 10 may be readily conveyed into a wellbore, and through relatively small wellbore restrictions.

A slurry mixture of swellable particles 18 and a slurry fluid is stored within the tubular body 12 adjacent the inflatable structure 14. In the embodiment shown the slurry fluid comprises a fluid within which the swellable particles 18 do not swell. This arrangement therefore assists to prevent premature swelling of the swellable particles 18. The slurry fluid may be selected in accordance with the type of swellable particles 18 used. For example, if the swellable particles 18 are adapted to swell in water then the slurry fluid may comprise a high salinity water, oil or the like.

The slurry of swellable particles 18 is contained between a fixed lower plate 20 and an upper piston 22. When the seal 10 is located at the required depth within a wellbore, the slurry of swellable particles 18 may then be displaced through ports 24 and into the inflatable structure 14 by downward movement of the piston 22, as shown in FIG. 2. In this way, the inflatable structure 14 may be inflated by the swellable particles 18 to describe a larger outer diameter and thus be configured to establish an annular seal between the tubular body 12 and a bore wall (not shown).

As shown in FIG. 1, the ports 24 comprise a non-return valve arrangement 26 such that the slurry of swellable particles 18 is prevented or restricted from flowing from the inflatable structure back into the tubular body 12.

Referring again to FIG. 2, the inflatable structure 14 is permeable to the slurry fluid such that said fluid may pass therethrough, as indicated by arrow 28, to be released into the wellbore, leaving the swellable particles 18 contained within the inflatable structure 14. Furthermore, the inflatable structure 14 is permeable to an activator fluid contained within the wellbore, such that said activator fluid may pass through the inflatable structure 14, indicated by arrow 30, to become exposed to the swellable particles 18 to activate swelling. The activator fluid may comprise water, such as a relatively low salinity formation water.

Accordingly, the inflatable structure 14 may become inflated to establish an annular seal by a combination of receiving the swellable particles 18 and swelling of the particles 18. Thus, relatively high expansion ratios may be achieved without compromising sealing integrity.

It may be necessary to circulate a fluid through the tubular member 12 after the inflatable structure 14 has been inflated to define a seal. Accordingly, in the embodiment shown the plate 20 is adapted to be released from the tubular body 12 and downwardly displaced. For example, the piston may be adapted to be actuated to shear the plate 20 from the tubular body, and then displace the plate 20 downwards. The tubular body may comprise a lower region of slightly increased inner diameter, such that location of the plate 20 and piston 22 within this region of increases diameter will permit fluid by-pass to be achieved.

In alternative arrangements, at least one of the plate and piston 22 may comprise a bust-disk arrangement adapted to be ruptured to permit fluid to pass therethrough.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention. For example, the swellable particles may be supplied from surface level, for example via a conduit or via a sealed container which may permit release of the particles when at the location of the seal.

Additionally, the seal itself may comprise the activating fluid to activate swelling of the particles. For example, a volume of swell activating fluid may be positioned above the swellable particles, such that the activating fluid may be displaced into the inflatable structure after the swellable particles. 

1. A downhole seal comprising an inflatable structure adapted to receive a volume of swellable particles at a downhole location.
 2. The downhole seal according to claim 1, wherein the downhole seal is adapted to permit the swellable particles to become exposed to an activator to initiate swelling of said particles.
 3. The downhole seal according to claim 1, wherein the inflatable structure is adapted to permit fluid communication of an activator fluid therethrough to expose the swellable particles to said activator fluid.
 4. The downhole seal according to claim 1, wherein at least a portion of the inflatable structure is permeable.
 5. The downhole seal according to claim 1, wherein the inflatable structure comprises an osmotic membrane adapted to establish fluid communication across said membrane by osmotic action.
 6. The downhole seal according to claim 1, wherein the inflatable structure defines at least one fluid port.
 7. The downhole seal according to claim 1, further comprising a store of a swelling activator, wherein the inflatable structure is adapted to receive the swelling activator from said store.
 8. The downhole seal according to claim 7, wherein the store of swelling activator is provided at surface level and/or in the region of the inflatable structure.
 9. The downhole seal according to claim 1, further comprising a store of swellable particles, wherein the inflatable structure is adapted to receive swellable particles from said store.
 10. The downhole seal according to claim 9, wherein the store of swellable particles is provided remotely from the inflatable structure and/or located adjacent the inflatable structure.
 11. The downhole seal according to claim 9, further comprising a communication passage between the inflatable structure and the store of swellable particles.
 12. The downhole seal according to claim 9 further comprising a displacing arrangement adapted to displace swellable particles from the store towards the inflatable structure.
 13. The downhole seal according to claim 1, further comprising a tubular body, wherein the inflatable structure is mounted on the tubular body.
 14. The downhole seal according to claim 13, wherein the tubular body comprises a store of swellable particles, such that swellable particles contained within the tubular body may be delivered to the inflatable structure to inflate said inflatable structure.
 15. The downhole seal according to claim 14, further comprising a displacing arrangement mounted within the tubular body and adapted to displace swellable particles from the store towards the inflatable structure.
 16. The downhole seal according to claim 15, wherein the displacing arrangement is adapted to be configured to permit circulation of a fluid through the tubular body and past the displacing arrangement.
 17. The downhole seal according to claim 16, wherein the displacing arrangement comprises a piston, and the tubular body comprises a region of increased diameter, wherein location of the piston within said region of increased diameter permits by-pass of fluid.
 18. The downhole seal according to claim 1, further comprising a slurry of swellable particles adapted to be delivered to the inflatable structure, wherein the slurry is formed by a volume of swellable particles mixed with a fluid.
 19. The downhole seal according to claim 18, wherein the fluid is selected to prevent swelling of the swellable particles.
 20. The downhole seal according to claim 18, wherein the slurry fluid comprises a high salinity fluid.
 21. The downhole seal according to claim 18 wherein the inflatable structure is adapted to permit release of the slurry fluid, thus permitting the swellable particles to become exposed to a swell activating medium.
 22. The downhole seal according to claim 1, wherein the inflatable structure comprises a swellable material.
 23. A method of establishing a downhole seal, said method comprising the steps of: locating an inflatable structure within a wellbore; and inflating said inflatable structure with swellable particles.
 24. The method according to claim 23, further comprising the step of exposing at least a portion of the swellable particles to a swell-activating medium.
 25. The method according to claim 23, comprising the step of running the inflatable structure through a wellbore restriction, and then inflating said inflatable structure. 